The present invention relates generally to a liquid crystal display, and more particularly to a liquid crystal display in which display operation is performed by driving liquid crystal molecules in a plane parallel to a substrate of the liquid crystal display.
Such type of liquid crystal display is disclosed, for example, in xe2x80x9cField effects in nematic liquid crystals obtained with interdigital electrodesxe2x80x9d, by R. A. Soref, Journal of Applied Physics, vol. 45, No. 12, December 1974, which liquid crystal display is hereafter referred to as Prior Art Example 1. In the Prior Art Example 1, there are described basic principles of driving liquid crystal molecules, such as what electric field should be applied to the liquid crystal molecules to rotate the liquid crystal molecules within a plane parallel to a substrate and the like.
Also, taking the basic principles described in the Prior Art Example 1 into consideration, Japanese examined patent publication No. 63-21907 discloses a liquid crystal display in which there is provided a switching element for each pixel, which liquid crystal display is hereafter referred to as Prior Art Example 2.
However, in these two Prior Art Examples, only basic principles, operation and the like are described, and there are still various problems in practicability. Therefore, taking these basic principles into consideration, various research have been done aiming at an electrode structure, alignment direction of liquid crystal molecules, contrast characteristic, and the like.
For example, there is known a liquid crystal display disclosed in Japanese patent laid-open publication No. 1-1200528 which aims at improving a switching characteristic and enabling a high speed operation, which liquid crystal display is hereafter referred to as Prior Art Example 3. In this liquid crystal display, a pair of electrodes are provided in each of an upper substrate and a lower substrate. These electrodes are switched to produce two kind of electric fields and, thereby, alignment direction of liquid crystal molecules is switched at high speed. However, in the structure of the Prior Art Example 3, it is necessary to individually control respective electrode pairs disposed on the upper substrate and the lower substrate, and there are many other problems.
On the other hand, there is known a liquid crystal display disclosed in Japanese patent publication No. 2743293, which liquid crystal display is hereafter referred to as Prior Art Example 4. In this patent publication, there is described a result of research on an initial alignment direction, and relationship between a twist angle and a distribution of contrast characteristic, taking alignment direction of liquid crystal molecules into consideration. However, in the liquid crystal display of the Prior Art Example 4, a conventionally proposed interdigital electrode structure is used and no improvement is made on the electrode structure. In other words, in the Prior Art Example 4, statistics were obtained on electric field caused by the conventional interdigital electrode structure and relationship between the initial alignment direction of liquid crystal molecules and contrast characteristic, and confirmation was made on the effect obtained by such structure. Therefore, the Prior Art Example 4 is valuable as a research result, but does not propose a new technology for liquid crystal display. In the Japanese patent publication No. 2743293, although it is described that an active matrix type liquid crystal display is realizable by using this structure, no proposition is made on a structure of an electrode therefore.
Thereafter, in Japanese patent laid-open publication No. 6-148596, there is proposed an active matrix type liquid crystal display with a concrete electrode structure, which liquid crystal display is hereafter referred to as Prior Art Example 5. In the liquid crystal display of the Prior Art Example 5, thin film transistors (TFT""s) are use as active elements, and a structure of electrodes including the active elements is described in this publication. More particularly, in the Prior Art Example 5, basically, two electrodes disposed parallel with each other are used in each pixel. Between the two electrodes, an electric field is produced and, thereby, liquid crystal molecules are rotated in a plane parallel with a substrate. However, in the Japanese patent laid-open publication No. 6-148569, a description is included which refers to the merit of not using transparent electrodes and, therefore, consideration is not given on aperture ratio and the like.
In the Prior Art Example 1 through Prior Art Example 5 mentioned above, liquid crystal molecules are driven such that the liquid crystal molecules rotate in a plane parallel with a substrate to perform display operation. Therefore, when compared with TN mode and the like in which liquid crystal molecules are driven between horizontal condition and vertical condition to perform display operation, it is expected that better viewing angle characteristics can be obtained by the liquid crystal displays of the Prior Art Examples 1 through 5. Hereafter, an operating mode in which liquid crystal molecules are rotated in a plane parallel to the substrate to perform display operation is called In-Plain Switching (IPS).
However, the Prior Art Example 1 through Prior Art Example 5 have various problems to be solved such as low aperture ratios and the like caused by the interdigital electrode structure, and it is difficult obtain such superior performance in practical use as to completely replace liquid crystal displays having TN mode with such IPS type liquid crystal displays.
After a proposition of the Prior Art Example 5, various IPS mode liquid crystal displays are proposed in which merits of the TN mode and the like are retained and demerits of the IPS mode are improved and which have high display characteristics not only in theory but also in practical use.
For example, considering an electrode structure and an electrode material and aiming at improving brightness of a displayed image, Japanese patent laid-open publication No. 9-61842 discloses a liquid crystal display, which is hereafter referred to as Prior Art Example 6. As mentioned above, a conventional electrode structure for IPS mode generally had a pair of interleaved sets of parallel strip-shaped fingers to constitute an interdigital structure. As a result thereof, when a liquid crystal display panel is viewed from the front of the panel, the proportion of the area where the electrodes are not disposed to the total pixel area becomes inevitably small. Also, chromium (Cr) generally used as a material of the electrodes shades light, and therefore it was impossible to obtain high aperture ratio. On the other hand, in the Prior Art Example 6, a transparent material, for example, ITO and the like, which is used as a material of a common electrode of a conventional liquid crystal display of TN mode and the like is used as a material for electrodes. Thereby, unnecessarily shaded area in each pixel area can be decreased and the aperture ratio of each pixel is substantially increased. However, in the Prior Art Example 6, the structure of the electrodes themselves is not changed, and new technology is not proposed except that the transparent material is used as a material of the electrodes.
To improve both a response speed and a transmittance of liquid crystal display, there are proposed liquid crystal displays in Japanese patent laid-open publication No. 11-64892, which is hereafter referred to as Prior Art Example 7, and in xe2x80x9cHigh-Transmittance, Wide-Viewing-Angle Nematic Liquid Crystal Display Controlled by Fringe-Field Switchingxe2x80x9d, by S. H. Lee, et al., ASIA DISPLAY ""98 INTERNATIONAL DISPLAY RESEARCH CONFERENCE, pp. 371-374, Sep. 28-Oct. 1, 1998, which is hereafter referred to as Prior Art Example 8. Each of these Prior Art Example 7 and Prior Art Example 8 discloses a technology somewhat similar to that of the Prior Art Example 6, and proposes ratios of various sizes to obtain good display characteristics to improve the liquid crystal display of the above-mentioned Prior Art Example 6, taking relationship between the ratios of various sizes such as electrode widths, the distance between electrodes and the like and display characteristics into consideration. Both in the Prior Art Example 7 and the Prior Art Example 8, both pixel electrodes and common electrodes are made of transparent materials to improve aperture ratio, similarly to the Prior Art Example 6.
On the other hand, in order to improve display irregularity and unsymmetry of viewing angle characteeristics, Japanese patent laid-open publication No. 10-319434 discloses a liquid crystal display which uses an electrode structure different from that of the conventional liquid crystal displays, which is hereafter referred to as Prior Art Example 9.
In the Prior Art Example 9, two problems to be solved are described. One of them is caused because no conductive film exists on a substrate, that is, an opposing substrate, on which electrodes are not disposed, in a conventional liquid crystal display panel having IPS mode. For example, when an electrified person touches the opposing substrate, electric charges move from the person to the substrate, and the opposing substrate is locally electrified. In such case, since no conductive film is formed on the opposing substrate, unintended electric field parallel to the substrate arises due to the electric charges existing locally. If liquid crystal molecules are rotated by the unintended electric field, there is a possibility, for example, that light passes through the liquid crystal display panel although the panel should display black. Therefore, display irregularity arises. Another problem of the Prior Art Example 9 concerns control of a tilt angle. For example, when anti-parallel rubbing is performed, a pretilt angle arises in liquid crystal molecules near a alignment film or layer due to the rubbing process and the like, so that whole liquid crystal layer has a tilt angle. Therefore, direction of viewing the liquid crystal molecules differs depending on the angle at which a person looks onto the panel, and viewing angle characteristics become unsymmetrical with respect to the front surface of the panel.
In order to solve these two problems, in the Prior Art Example 9, there is provided an electrode on the opposing substrate, in addition to the conventional structure required for the IPS mode. In operation of the liquid crystal display of the Prior Art Example 9, liquid crystal molecules are rotated in a plane parallel to the substrate in a manner similar to the conventional liquid crystal display of the IPS mode. Also, a component of an electric field which is perpendicular to the substrate is increased by the newly added electrode, and the liquid crystal molecules are also controlled in a direction perpendicular to the substrate, thereby decreasing a tilt angle. To realize such operation, liquid crystal molecules are used which have a negative anisotropy of permittivity. By using such structure, it is possible to obtain viewing angle characteristics which are symmetrical with respect to the front surface of the panel. Also, when such newly added electrode is provided on whole surface of the opposing substrate, even if the surface of the opposing substrate is locally electrified, the influence of such electrification can be obviated by the newly added electrode. Therefore, the problem of display irregularity caused by the unintended electric field can be obviated.
As a reference technology, description will be made on a liquid crystal display disclosed in Japanese patent laid-open publication No. 9-325346, which is hereafter referred to as Prior Art Example 10.
As mentioned above, it is conventionally known that a liquid crystal display of the TN mode and the like has relatively narrow viewing angle characteristics, but, by using a technology of rotating liquid crystal molecules in a plane horizontal with respect to the substrate, such as the IPS mode technology, wide viewing angle characteristics can be obtained. Therefore, in the Prior Art Example 10, user can switch between these two viewing angle characteristics in accordance with the purpose of using the liquid crystal display, and four kinds of electrodes are provided every pixel. Among these electrodes, the first through the third electrodes are provided on one of a pair of opposing substrates, and the fourth electrode is provided on the other substrate. More particularly, the first electrode disposed on one of the substrates and the fourth electrode disposed on the other substrate constitute a pixel electrode and an opposing electrode, and the second and third electrodes constitute the pixel electrode and the common electrode used in the above-mentioned Prior Art Example 1 through Prior Art Example 9. Also, in order to independently control an electrode pair of the first and fourth electrodes and an electrode pair of the second and third electrodes, the first through the third electrodes are independently disposed in each pixel, and two switching elements are provided every pixel.
As can be understood from the above-mentioned brief explanation, the Prior Art Example 10 is for a special use, and has the structure slightly differ from that of each of the abovementioned Prior Art Example 1 through Prior Art Example 9. Also, in the Prior Art Example 10, since the first through the third electrodes are independently disposed in each pixel and two switching elements are provided every pixel, the liquid crystal display of the Prior Art Example 10 is not practical in a manufacturing cost and the like.
The Prior Art Example 10 was explained above only for reference when reviewing documents concerning liquid crystal displays.
When compared only the cross sectional structures of the liquid crystal display panels shown in the Prior Art Example 9 and the Prior Art Example 10, it may be seen as if they concern the same technology. However, they disclose quite different technologies, and operate differently. Those of ordinary skill in the art clearly understand the difference between these Prior Art Examples from the specifications thereof.
In other words, in order to gasp respective technologies of the liquid crystal displays, it is not appropriate to consider only the cross sectional structure in a pixel area shown in the drawing. It is necessary to consider all portions of the description describing characteristic features of the liquid crystal display. Considering these points, problems of the Prior Art Example 1 through Prior Art Example 9 are summarized as the problems to be solved by the present invention.
As mentioned above, each of all the Prior Art Example 1 through Prior Art Example 9 utilizes a potential difference between two kinds of electrodes disposed parallel to each other to form an electric field parallel to the substrate.
However, the electric field generated in this way becomes parallel to the substrate in the vicinity of the electrodes, but often becomes round and arc shaped as it becomes near the opposing substrate.
In such case, in the Prior Art Example 1 through Prior Art Example 8, the arc shaped electric field give influence on other layer or layers formed on the opposing substrate, and on the inside of the substrate. For example, as another layer formed on the opposing substrate, there is a layer comprising organic material and the like such as a color layer for performing color display. However, the layer comprising such material has the property that it is easily electrified and has a residual potential. Therefore, when the layer such as the color layer is influenced by the arc shaped electric field, an unintended potential difference appears in the color layer and such potential difference remains therein for a relatively long time. As a result, when a different image signal is written into a pixel electrode in a subsequent cycle time, it is impossible to produce a desired electric field because of the electric field caused by the residual electric charges, so that precise display is not realized.
On the other hand, in the Prior Art Example 9, there is a possibility that arc shaped electric field is produced in the vicinity of the opposing substrate. However, in the Prior Art Example 9, since the electrode is formed on the surface of the opposing substrate on the side of a liquid crystal material layer, the arc shaped electric field does not give influence on the color layer disposed on the opposing substrate or on the inside portion of the opposing substrate. Therefore, the abovementioned problem of the Prior Art Examples 1 through 8 does not occur in the Prior Art Example 9.
However, although the electrode disposed on the opposing substrate in the Prior Art Example 9 can solve the problem of the Prior Art Example 1 through Prior Art Example 8, the electrode does not function to directly avoid an influence of the electric field from the liquid crystal layer to the opposing substrate. As mentioned above, the electrode disposed on the opposing substrate in the Prior Art Example 9 mitigates the influence toward the side of the liquid crystal layer caused when the opposing substrate is locally electrified by external cause, and the electrode is formed mainly for controlling a tilt angle of liquid crystal molecules in the liquid crystal layer on the side of the opposing substrate. Here, if only the former problem is to be solved, it is not always necessary to provide the electrode on the opposing substrate on the side of the liquid crystal layer. It is also possible that the electrode is disposed on the most outer side, that is, on the side of a viewer or a user of the liquid crystal display. Therefore, the reason why the electrode formed on the opposing substrate must exist on the side of the liquid crystal layer is to perform the latter object, that is, to control the tilt angle of the liquid crystal molecules.
When the control of the tilt angle in the Prior Art Example 9 is considered, control of a potential voltage supplied to the electrode disposed on the opposing substrate becomes complicated. Generally, as an image signal, an alternative current (AC) signal is applied to each pixel electrode. Also, in order to precisely control a tilt angle, it is necessary to consider not only a direction of an electric field to be produced but also a required intensity of the electric field. Further, it is well known that an intensity of an electric field is determined by relationship of a potential difference and a distance. Considering these items and in order to precisely control the tilt angle in the Prior Art Example 9, it is necessary to vary a potential voltage applied to the electrode disposed on the opposing substrate in accordance with an image signal.
Considering the above-mentioned technologies disclosed in the Prior Art Example 1 through Prior Art Example 9, it is an object of the present invention to provide a novel liquid crystal display which does not require complicated control of a voltage signal and the like described in the Prior Art Example 9 and which does not have the disadvantages of the Prior Art Example 1 through Prior Art Example 8.
It is another object of the present invention to provide a liquid crystal display which has superior display characteristics.
It is still another object of the present invention to provide a liquid crystal display in which alignment direction or directions of liquid crystal molecules can be efficiently and easily controlled.
It is another object of the present invention to provide a liquid crystal display in which it is possible to prevent an electric field for driving liquid crystal molecules from affecting an inside portion of an opposing substrate and various layers such as a color filter layer and the like.
It is still another object of the present invention to provide a liquid crystal display which can be easily manufactured.
In order to solve the above-mentioned problems, the inventors of the present invention carefully considered on the Prior Art Example 1 through Prior Art Example 9, and obtained the following conclusion.
In order to solve the problems of the technology of the Prior Art Example 1 through Prior Art Example 8, it is necessary to provide a conductor layer (electrode) on an opposing substrate. By disposing such conductive layer (electrode), an electric field which includes large component perpendicular to a substrate is produced between a pixel electrode and the conductive layer (electrode) or between a common electrode and the conductive layer (electrode).
However, in each of the Prior Art Example 1 through Prior Art Example 9, the pixel electrode and the common electrode are disposed such that an electric field parallel with the substrate is produced. Therefore, by such structure, a superposed electric field, that is, an electric field which actually gives an influence on liquid crystal molecules, is not an electric field parallel with the substrate. Also, in such condition, in order to rotate the liquid crystal molecules in a plane parallel with the substrate, complicated control is required on the electrode disposed on the side of the opposing substrate, as can be seen from the Prior Art Example 9.
Therefore, in the present invention, liquid crystal molecules having a negative anisotropy of permittivity are used, and an electric field including large component which is perpendicular to the substrate is produced between the pixel electrode and the common electrode. By using a synthesized electric field which is obtained by superposing such electric field and an electric field produced between the pixel electrode and the electrode disposed on the opposing substrate, the liquid crystal molecules are controlled such that the liquid crystal molecules are driven in a plane parallel with the substrate.
That is, an electric field produced between the pixel electrode and the common electrode is assumed to be a first electric field, and an electric field produced between the pixel electrode and the electrode disposed on the opposing substrate is assumed to be a second electric field. In such case, liquid crystal molecules near the substrate on which the pixel electrode is disposed and liquid crystal molecules near the opposing substrate are easily influenced by the first electric field and the second electric field, respectively, but, because of the property of the liquid crystal molecules, operation in the direction perpendicular to the substrate are restrained by each other. More particularly, liquid crystal molecules near the substrate on which the pixel electrode and the like are disposed are easily influenced by the first electric field, tend to rotate in a plane parallel to the substrate, and form a first predetermined tilt angle in a direction perpendicular to the substrate. On the other hand, liquid crystal molecules near the opposing substrate are easily influenced by the second electric field, tend to rotate in a plane parallel to the substrate in manner similar to the liquid crystal molecules mentioned above, and form a second predetermined tilt angle in a direction perpendicular to the substrate. Here, when the surface of the substrate is considered as a reference plane, the second predetermined tilt angle and the first predetermined tilt angle differ from each other in polarity of angles. However, since liquid crystal molecules has viscoelasticity as its property, operation for forming the first predetermined tilt angle and operation for forming the second predetermined tilt angle are mutually influenced and restrained. In this way, change of alignment toward a direction perpendicular to the substrate is strongly suppressed, and liquid crystal molecules can smoothly rotate in a plane parallel to the substrate. Thereby, superior alignment can be maintained in optical characteristics.
Considering the above-mentioned influence of the electric field on liquid crystal molecules, in the present invention, the electrode disposed on the opposing substrate also functions as a kind of a common electrode. In the present invention, these two kinds of common electrodes are mutually distinguished by the substrates on which such common electrodes are disposed. That is, one of the common electrode disposed on the substrate on which the pixel electrodes are disposed is called a first common electrode, and the other common electrode disposed on the opposing substrate is called a second common electrode.
In practice, the present invention provides a liquid crystal display which uses a novel method of driving liquid crystal molecules mentioned below, as a means for solving the problems mentioned above.
According to an aspect of the present invention, there is provided a liquid crystal display having a first substrate, a second substrate parallel opposed to the first substrate, and a liquid crystal layer including liquid crystal molecules, wherein display operation is performed by changing a director of the liquid crystal molecules mainly in a plane parallel to the first and second substrate, the liquid crystal display comprising: a first common electrode which is disposed on the side of the first substrate and which receives a first predetermined potential; an insulating layer formed on the first common electrode; at least one pixel electrodes each of which is formed on the insulating layer and has a plurality of opening portions; a second common electrode which is disposed on the side of the second substrate and which receives a second predetermined potential; wherein the liquid crystal molecules have a negative anisotropy of permittivity; and wherein the first common electrode comprises at least a particular portion formed in a particular area which extends from a non-opening portion to an opening portion of the pixel electrode and in which the first common electrode overlaps the non-opening portion in a cross section perpendicular to the substrates.
In this first liquid crystal display, a first predetermined potential is applied to the first common electrode, and a second predetermined potential is applied to the second common electrode. More particularly, the first predetermined potential produces a first electric field comprising a first horizontal electric field component which is horizontal (parallel) with the substrate and a first vertical component which is vertical with the substrate, between the first common electrode and the pixel electrode, when a voltage is applied to the pixel electrode to drive the pixel. Also, the second predetermined potential produces a second electric field comprising a second horizontal electric field component which is horizontal (parallel) with the substrate and a second vertical component which is vertical with the substrate, between the second common electrode and the pixel electrode, when a voltage is applied to the pixel electrode to drive the pixel. When the first and second predetermined potentials are applied to the first and second common electrode and thereby the first and second electric field are produced, these electric fields are superposed on each other and, as a result thereof, give influence on liquid crystal molecules in the liquid crystal layer in a manner mentioned above.
In this case, it is preferable that the first common electrode is formed on the first substrate, and wherein the particular portion of the first common electrode has, in a cross section perpendicular to the substrates, a shape which covers whole area corresponding to the plurality of opening portions on the first substrate.
It is also preferable that the first common electrode comprises, in a cross section perpendicular to the substrates, common electrode side opening portions in an area which overlaps with the non-opening portion of the first substrate.
It is further preferable that the first common electrode is formed on the first substrate, and has a shape which covers the first substrate every pixel.
It is advantageous that the second common electrode is formed on whole area of the second substrate.
It is also advantageous that a portion of the first common electrode corresponding to one pixel is directly coupled with a portion of the first common electrode corresponding to anther pixel which is adjacent to the one pixel in a predetermined direction.
It is further advantageous that the liquid crystal display further comprises an auxiliary conductive portion which is formed of a conductive material having lower resistivity than that of a conductive material forming the first common electrode and which is coupled with the first common electrode.
It is preferable that the liquid crystal display further comprises: a plurality of auxiliary conductive portions each of which is formed of a conductive material having lower resistivity than that of a conductive material forming the first common electrode; wherein the first common electrode is constituted of first common electrode portions each of which is provided for a pixel; and wherein each of the auxiliary conductive portions couples the first common electrode portions which are adjacent with each other in a predetermined direction.
It is also preferable that the liquid crystal display is an active matrix type liquid crystal display which comprises a switching element for each pixel.
It is further preferable that the switching element is a thin film transistor.
It is advantageous that the auxiliary conductive portion is formed in the same layer as that of the gate electrode of the thin film transistor.
It is also advantageous that the auxiliary conductive portion is formed by patterning an electrode material of the gate electrode, in the same process step as that of the gate electrode.
It is further advantageous that the first predetermined potential and the second predetermined potential are mutually equal potential.
It is preferable that the first substrate, the second substrate and the liquid crystal layer compose a liquid crystal display panel; and wherein the first common electrode and the second common electrode are coupled with each other at a peripheral portion of the liquid crystal display panel.
It is also preferable that the liquid crystal display further comprises a potential adjusting means which adjust the first predetermined potential and the second predetermined potential applied to the first and second common electrodes.
It is further preferable that the second common electrode is formed of a transparent electrode material; and wherein at least one of the pixel electrodes and the first common electrode is also formed of a transparent electrode material.
It is advantageous that each of the plurality of opening portions of the pixel electrode has a parallelogram shape; and wherein an angle between a direction along short sides of the parallelogram and a direction along long sides of the parallelogram is smaller than an angle between the alignment direction of the liquid crystal molecules and the direction along long sides of the parallelogram.
It is also advantageous that each of the plurality of opening portions of the pixel electrode has a parallelogram shape; and wherein the alignment direction of the liquid crystal molecules is determined to be a direction perpendicular to a direction of long sides of the parallelogram.
It is further advantageous that the plurality of opening portions are grouped into two groups; and wherein, in the plurality of opening portions of the two groups, long sides of parallelogram shapes of the opening portions of both groups extend in the same direction, and short sides thereof are disposed symmetrically with respect to a line having a direction perpendicular to the direction of the long sides.
It is preferable that each of the plurality of opening portions of the pixel electrode has a V-shape having short sides located along the alignment direction of the liquid crystal molecules and composed by combining two parallelograms which share a short side with each other and whose long sides are disposed symmetrically with respect to the alignment direction.
It is also preferable that the liquid crystal display further comprises: a color layer for realizing color display on the side of the second substrate; and wherein the color layer is formed as a layer which is farther from the liquid crystal layer than the second common electrode.
According to another aspect of the present invention, there is provided a liquid crystal display having a first substrate, a second substrate opposed to the first substrate, and a liquid crystal layer including liquid crystal molecules, wherein display operation is performed by changing a director of the liquid crystal molecules mainly in a plane parallel to the first or second substrate, the liquid crystal display comprising: a first common electrode which is disposed on the side of the first substrate and which receives a first predetermined potential; an insulating film formed on the first common electrode; at least one pixel electrodes each of which is formed on the insulating film and has a plurality of opening portions; a second common electrode which is disposed on the side of the second substrate and which receives a second predetermined potential; wherein the liquid crystal molecules have negative anisotropy of permittivity; and wherein when a drive potential is applied to the pixel electrode to drive a pixel having the pixel electrode, the first common electrode together with the pixel electrode produce a first electric field including a first component which is perpendicular to the substrates, and the second common electrode together with the pixel electrode produce a second electric field including a second component which is perpendicular to the substrates and which has a direction opposite to that of the first component, the first and second electric fields are superposed to produce an electric field which drive the liquid crystal molecules in a plane parallel to the substrates.
According to still another aspect of the present invention, there is provided, in a liquid crystal display having a first substrate, a second substrate opposed to the first substrate, and a liquid crystal layer including liquid crystal molecules, wherein display operation is performed by changing a director of the liquid crystal molecules mainly in a plane parallel to the first or second substrate, a method of performing display operation comprising: forming a first common electrode on the side of the first substrate; forming an insulating film on the first common electrode; forming at least one pixel electrodes on the insulating film, each of the at least one pixel having a plurality of opening portions; forming a second common electrode on the side of the second substrate; forming an liquid crystal display panel of the liquid crystal display by using liquid crystal molecules have a negative anisotropy of permittivity; applying a first predetermined potential to the first common electrode such that when a drive potential is applied to the pixel electrode to drive a pixel having the pixel electrode, the first common electrode together with the pixel electrode produce a first electric field including a first component which is perpendicular to the substrates; applying a second predetermined potential to the second common electrode such that when a drive potential is applied to the pixel electrode to drive a pixel having the pixel electrode, the second common electrode together with the pixel electrode produce a second electric field including a second component which is perpendicular to the substrates and which has a direction opposite to that of the first component; and superposing aid first and second electric fields in the liquid crystal layer, wherein, by using viscoelasticity of liquid crystal molecules, a component of operation in a direction perpendicular to the substrates in an operation in which liquid crystal molecules near the first substrate liable to be influenced by the first electric field are going to rotate in a plane horizontal with the substrate and are going to form a first predetermined tilt angle in a direction perpendicular to the substrates, and a component of operation in a direction perpendicular to the substrates in an operation in which liquid crystal molecules near the second substrate liable to be influenced by the second electric field are going to rotate in a plane horizontal with the substrate and are going to form a second predetermined tilt angle in a direction perpendicular to the substrates, the second predetermined tilt angle being opposite in direction to the first predetermined tilt angle, are influenced and restrained by each other, thereby rotating the liquid crystal molecules a plane parallel to the substrates.
In this case, it is preferable that the first predetermined potential and the second predetermined potential are equal to each other.
It is also preferable that a portion of the first common electrode corresponding to one pixel is directly coupled with a portion of the first common electrode corresponding to anther pixel which is adjacent to the one pixel in a predetermined direction.
It is further preferable that the method further comprises forming a plurality of auxiliary conductive portions each of which is formed of a conductive material having lower resistivity than that of a conductive material forming the first common electrode; wherein the first common electrode is constituted of first common electrode portions each of which is provided for a pixel; and wherein each of the auxiliary conductive portions couples the first common electrode portions which are adjacent with each other in a predetermined direction.